This invention relates generally to injection molding and more particularly to a cold runner injection molding nozzle which effectively cools the liquid molding material flowing through it.
Modern hot runner injection molding systems require a number of nozzles through which melt flows from a melt distribution manifold to the different gates. Nozzles which are heated by an integral electrical heating element with a helical portion encircling a central melt channel to heat the melt flowing through the channel are well known for molding thermoplastic materials. An example of such a heated nozzle is shown in the applicant's U.S. Pat. No. 4,403,405 which issued Sep. 13, 1983.
However, when molding materials such as two-component silicon rubber or other liquid molding materials which are thermosetting rather than thermoplastic and have cool runners rather than hot runners, the two components are mixed just before injection into a cavity in a hot mold. This requires that the mold must be heated rather than cooled and the molding material must be retained well below its cross-linking temperature as it flows through the nozzle. An example of apparatus for molding thermosetting materials is seen in German Patent Application Number P23 41 589.6 to Delbrouck which was laid-open Aug. 17, 1973. However, in that case, the liquid molding material flows around an elongated probe through which cooling water flows. In other words, the liquid molding material flows between the cooled probe and the heated mold which has the disadvantage that the temperature of the liquid molding material is not very uniform because it is cooler near the inside and hotter near the outside.